...why is windows, or any other OS for that matter, not good for developing in Ruby? Where I work our desktops are all Windows, and we have written a few ruby apps. It's not like Ruby requires anything special... a decent syntax editor and that's about it. Eclipse handles Ruby, Sublime Text, Ultra Edit... etc...

I'm guessing it's because a lot of Ruby stuff is based on cli and the Windows console is, well, less than good.
I don't think stuff like RVM (which is the only sane way of using ruby/rails) and Capistrano even run on Windows.